1. Field of the Invention
The present invention relates generally to a torque detecting system for a bicycle, and more specifically to a torque detecting system for a bottom bracket axle of a power-assisted bicycle and a two-phase signal transmitting method using the aforesaid torque detecting system.
2. Description of the Related Art
A conventional electrical power-assisted bicycle is equipped with an electrical motor adapted either to power the bicycle or to assist with pedaling. Usually, the power-assisted bicycle has a built-in torque detecting system including a strain gauge for detecting a torque applied on the bicycle, and a controller for determining whether or not the power applied on the pedal by the bicyclist is sufficient based on the detected torque. In a conventional design, the strain gauge is attached on a bicycle frame of the power-assisted bicycle in order to transmit the detected signal to the controller precisely. This design has however a drawback that the power applied on the bicycle by the bicyclist to the bicycle can not be measured precisely by reference to the torque received by the bicycle frame. In another conventional design, the strain gauge is attached on a bottom bracket axle connected with a crank that is driven by a pedal and the detected signal of the strain gauge is transmitted to the controller through a transducer mounted on the bicycle frame, such that the power applied on the bicycle by the bicyclist can be more precisely measured by reference to the detected signal of the strain gauge. However, this design has problems of signal attenuation and signal loss in the process of signal transmission because the strain gauge will move along with the rotary bottom bracket axle and the transducer is kept away from the strain gauge a certain distance, resulting in controller's miscalculation about the power applied by the bicyclist. In other words, it is desirable to provide a torque detecting system for a power-assisted bicycle, which can eliminate the aforesaid drawbacks.